Chapter 6
Acellular Pathogens
Figure 6.1 The year 2014 saw the first large-scale outbreak of Ebola virus (electron micrograph, left) in human
populations in West Africa (right). Such epidemics are now widely reported and documented, but viral epidemics are
sure to have plagued human populations since the origin of our species. (credit left: modification of work by Thomas
W. Geisbert)
Chapter Outline
6.1 Viruses
6.2 The Viral Life Cycle
6.3 Isolation, Culture, and Identification of Viruses
6.4 Viroids, Virusoids, and PrionsIntroduction
Public health measures in the developed world have dramatically reduced mortality from viral epidemics. But when
epidemics do occur, they can spread quickly with global air travel. In 2009, an outbreak of H1N1 influenza spread
across various continents. In early 2014, cases of Ebola in Guinea led to a massive epidemic in western Africa. This
included the case of an infected man who traveled to the United States, sparking fears the epidemic might spread
beyond Africa.
Until the late 1930s and the advent of the electron microscope, no one had seen a virus. Yet treatments for preventing
or curing viral infections were used and developed long before that. Historical records suggest that by the 17th
century, and perhaps earlier, inoculation (also known as variolation) was being used to prevent the viral disease
smallpox in various parts of the world. By the late 18th century, Englishman Edward Jenner was inoculating patients
with cowpox to prevent smallpox, a technique he coinedvaccination.[1]
Today,thestructureandgeneticsofvirusesarewelldefined,yetnewdiscoveriescontinuetorevealtheircomplexities.
In this chapter, we will learn about the structure, classification, and cultivation of viruses, and how they impact their
hosts. In addition, we will learn about other infective particles such as viroids and prions.
- S. Riedel “Edward Jenner and the History of Smallpox and Vaccination.”Baylor University Medical Center Proceedings18, no. 1
(January 2005): 21–25.
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